A two-year study of the efficacy, stability and generalizability of a prediction model for work tolerance of workers wearing encapsulating protective clothing (PC) in moderate to warm environments is proposed. The project will test and refine a recently developed prediction model and determine the generalizability of this approach to prediction in various industrial situations. After medical screening, 50 subjects will be measured during a bench step test of less than 20 minutes duration at room temperature (WBGT = 18oC). Simple data (i.e. duration, comfort rating etc.) from this bench step will then be used to predict performance on a generic work protocol consisting of 15 min of treadmill walking at 3 mph followed by 5 min of arm curls with 14.6 kg of weight (referred to as "work" hereafter), with this work sequence repeated on separate days in counterbalanced order under these four conditions: 1) continuous work @ 300Kcal/hr at WBGT =- 18oC; 2) 30 min work at 300 Kcal/min succeeded by 30 min rest (time weighted avg of 180 Kcal/hr) at all WBGT = 18oC; 3) 30 min work @ 540 Kcal/min in WBGT = 26oC followed by 30 min rest in cool (WBGT = 18oC) w/o PC at time weighted WBGT = 27oC; 4) 30 min work @ 300 Kcal/hr followed by 30 min rest in PC in WBGT of 21oC. Models will be derived and tested for generalizability and stability by comparisons of models across subgroups and treatments. Proposed project addresses, in part, 5 of the 12 research needs listed in NIOSH Criteria for a Recommended Standard for Occupational Exposure to Hot Environments, Revised Criteria, 1986. Current guidance for worker safety in PC is limited.